! function(win) {


        


        var v, initial_scale, timeCode, dom = win.document,
            domEle = dom.documentElement,
            viewport = dom.querySelector('meta[name="viewport"]'),
            flexible = dom.querySelector('meta[name="flexible"]');


        function resize() {
            var domWidth = domEle.getBoundingClientRect().width;//可视区宽度
            if (domWidth / v > 540) {
                domWidth = 540 * v;
            }
            win.rem = domWidth / 16;
            domEle.style.fontSize = win.rem + "px";
        }

        if (viewport) {
            //viewport：<meta name="viewport"content="initial-scale=0.5, minimum-scale=0.5, maximum-scale=0.5,user-scalable=no,minimal-ui"/>
            var o = viewport.getAttribute("content").match(/initial\-scale=(["']?)([\d\.]+)\1?/);
            if (o) {
                initial_scale = parseFloat(o[2]);
                v = parseInt(1 / initial_scale);
            }
        } else {
            if (flexible) {
                var o = flexible.getAttribute("content").match(/initial\-dpr=(["']?)([\d\.]+)\1?/);
                if (o) {
                    v = parseFloat(o[2]);
                    initial_scale = parseFloat((1 / v).toFixed(2))
                }
            }
        }
        if (!v && !initial_scale) {
            var n = (win.navigator.appVersion.match(/android/gi), win.navigator.appVersion.match(/iphone/gi));
            v = win.devicePixelRatio;
            v = n ? v >= 3 ? 3 : v >= 2 ? 2 : 1 : 1, initial_scale = 1 / v
        }
        //没有viewport标签的情况下
        if (domEle.setAttribute("data-dpr", v), !viewport) {
            if (viewport = dom.createElement("meta"), viewport.setAttribute("name", "viewport"), viewport.setAttribute("content", "initial-scale=" + initial_scale + ", maximum-scale=" + initial_scale + ", minimum-scale=" + initial_scale + ", user-scalable=no"), domEle.firstElementChild) {
                domEle.firstElementChild.appendChild(viewport)
            } else {
                var m = dom.createElement("div");
                m.appendChild(viewport), dom.write(m.innerHTML)
            }
        }
        win.dpr = v;
        win.addEventListener("resize", function() {
            clearTimeout(timeCode), timeCode = setTimeout(resize, 300)
        }, false);
        win.addEventListener("pageshow", function(b) {
            b.persisted && (clearTimeout(timeCode), timeCode = setTimeout(resize, 300))
        }, false);
        resize();
    }(window);